1. Field of the Invention
The present invention relates to an information medium substrate that functions as a support for various functional layers of an information medium and to an information medium manufactured using such information medium substrate.
2. Description of the Related Art
One example of an information medium manufactured using this type of information medium substrate is the optical disc disclosed by Japanese Laid-Open Patent Publication No. 2001-43570. This optical disc includes a substrate produced by injection molding polycarbonate resin, a reflective film formed so as to cover an information recording surface of the substrate, and a protective film formed of an acrylic UV-curable resin so as to cover the reflective film. A stacking ring (a convex part that is ring-shaped in planar form) with a height of around 0.2 mm is formed on one surface of the substrate (i.e., a surface that is a rear surface of the information recording surface and is on the side of the optical disc where a laser beam used for reading, etc., is incident). A ring spacer (a convex part that is ring-shaped in planar form) with a height of around 0.3 mm is also formed on the surface of the protective film by screen printing using an acrylic UV-curable resin.
The stacking ring and the ring spacer described above are formed with the same diameter at overlapping positions in the thickness direction of the optical disc. Accordingly, when a plurality of optical discs are stacked, the protruding end part of the ring spacer of an optical disc positioned above will contact the protruding end part of the stacking ring of the optical disc positioned below. In this way, for each pair of adjacent optical discs that are above and below one another in a stack of optical discs, surface contact between the surface of the substrate of one optical disc and the surface of the protective film of the other optical disc is avoided. As a result, when a plurality of optical discs are stacked, a situation where the optical discs tightly contact one another and stick together and a situation where damage occurs for the substrate can be avoided.